Thermodynamic and Adsorption Behaviour of Medicinal Nitramine as a Corrosion Inhibitor for AISI Steel Alloy in HCl Solution

The inhibition ability of 2-amino-5-nitrothiazole (Nitramine) against the corrosion of AISI steel 4130 in 1 mol/L HCl solution was evaluated by polarization, electrochemical impedance spectroscopy (EIS) and chronoamperometry. Polarization studies indicated that nitramine retards both the cathodic and anodic reactions through chemical adsorption and blocks the active corrosion sites. The adsorption of this compound obeyed the Temkin's adsorption isotherm. The inhibition efficiency was increased with inhibitor concentration as well as temperature. EIS data were analysed by equivalent circuit model shows that as the inhibitor concentration increased the charge transfer resistance of steel increased whilst double layer capacitance decreased. Kinetic and thermodynamic parameters such as activation energy, enthalpy, entropy and free energy of activation and adsorption were calculated. Atomic force microscopy and optical microscopy were used to study the steel surface with and without inhibitor.